(not used to S7-300 in TIA)
You have a problem with the AO module. If you right click it and do "Online Diagnostics" you should get a more exact error.
You cannot use a v2.0 firmware CPU with TIA Portal.
You need a minimum 4MB memory card to upgrade the CPU firmware:
https://support.industry.siemens.com/cs/document/16750732/operating-system-updates-for-cpu-315-2dp?dti=0&lc=en-US
The instructions are for STEP 7 V5.x and PROMMER.
Or...
To avoid all that, use STEP 7 V5.x (V5.7 is the latest version) instead of TIA Portal.